Tobacco is conventionally fed from a source of cut tobacco to a cigarette-making machine by air conveying through a feed pipe at high speed, typically about 4000 ft/min (about 1300 m/min). The tobacco is air conveyed through the feed pipe to an air-lock separator wherein tobacco is separated from the conveying air and is accumulated therein as a stationary mass until a desired amount has been collected. The vacuum is shut off and the air lock opened to dump the stationary mass into the cigarette-making machine hopper.
Air conveying of tobacco at the high speeds required for reliable operation of this prior art system leads to degradation of the particle size of the tobacco and any degradation in particle size leads to loss of filling power of the tobacco, that is, the ability of the tobacco to fill the paper cigarette tube, and hence is detrimental.
Another difficulty of the prior art system is that some "hang up" of falling tobacco particles on the air lock door may occur during the dumping operation, and these particles result in incomplete sealing of the air lock closure, with the consequent development of leaks and the necessity for additional vacuum.